Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A1: Nuclear Spin Dynamics in Semiconductor Nanostructures |
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Sponsoring Units: DCMP Chair: Seigo Tarucha, University of Tokyo Room: LACC 152 |
Monday, March 21, 2005 8:00AM - 8:36AM |
A1.00001: Nuclear Spin Induced Oscillatory Current in Spin Blockaded Quantum Dots Invited Speaker: Hyperfine interactions between electron and nuclear spins in quantum dots are subject to intensive studies from the viewpoints of quantum computing. In this talk I will review our recent experimental studies for a GaAs-based double quantum dots in the spin blockade regime where the electron conduction is mostly blocked by Pauli effect unless the electron spin state is changed [1]. Thus a small leakage current observed in the spin-blockaded double dot can be a sensitive measure not only for electron spin-flip events but also for a nuclear spin states in the dot if the spin-flip is mediated by hyperfine interactions. We have observed the leakage current shows time-dependent oscillations and is significantly diminished by application of an AC magnetic field whose frequency can induce nuclear magnetic resonance for 71Ga and 69Ga nuclei [2]. A possible nuclear spin polarization mechanism due to hyperfine flip-flop scattering is proposed. [1] K. Ono et al., Science, 297, 1313 (2002). [2] K. Ono et al., Phys. Rev. Lett 92, 256803 (2004). cond-mat/0309062. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 9:12AM |
A1.00002: Electron-nuclear spin coupling in nano-scale devices: self-sustaining resistance oscillations and controlled multiple quantum coherences Invited Speaker: Author: G Yusa, K. Muraki, K. Takashina (NTT BRL), K. Hashimoto (SORST-JST), and Y. Hirayama (NTT BRL and SORST-JST). We studied electron-nuclear spin coupled systems implemented in microscopic fractional quantum Hall devices and found that in a constant voltage measurement, the longitudinal resistance of such devices oscillates self-sustainingly with a period of about 200 sec. Such behavior suggests that the average nuclear spin polarization self-sustainingly oscillates between randomized and polarized states. When the resistance is measured in constant current mode, on the other hand, nuclear spins are polarized and reach a steady state in about 200 sec. Using the polarized state as an initial state, quantum mechanical superpositional states between four nuclear spin states (multiple quantum coherence) are controlled by pulsed radio frequency radiation resonant with nuclear spin transitions (nuclear magnetic resonance, NMR). Any arbitrary multiple quantum coherent state can be detected as change in the longitudinal resistance. Our findings represent a big step closer to practical all-electrical solid state nuclear spin quantum computing and quantum memory devices. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:48AM |
A1.00003: Nuclear spin polarization and coherence in semiconductor nanostructures Invited Speaker: We have studied the mechanism of dynamical nuclear spin polarization by hyperfine interaction in the spin-blocked vertical double quantum dot system\footnote{C. Deng and X. Hu, cond-mat/0402428. To appear in Phys. Rev. B.}. We have calculated hyperfine transition rates between nuclear spin levels and solved the master equations for the nuclear spins in the double quantum dot. Specifically, we incorporated energy shifts and state mixing due to nuclear quadrupole coupling, which is present because of doping-induced local lattice distortion and strain in the vertical quantum dots. Our results show that doping-induced nuclear quadrupole coupling, together with hyperfine interaction, can cause significant nuclear spin relaxation in the quantum dot system under appropriate conditions (such as tunnel broadening of electronic levels). Therefore, we have found a new channel for nuclear spin relaxation/depolarization in strained material systems at low temperatures. We have also studied internal nuclear spin dynamics in quantum dots and quantum wells through dipolar coupling\footnote{C. Deng and X. Hu, cond-mat/0312208. Submitted to Phys. Rev. B; C. Deng and X. Hu, cond-mat/0406478. To appear in IEEE Trans. Nanotech.}. Our results show strong influences of any inhomogeneity in the hyperfine coupling on the nuclear spin dynamics. Our studies thus demonstrate theoretically the complexities of coupled electron-nuclear spin dynamics in semiconductor nanostructures. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:24AM |
A1.00004: Controlling Nuclear Spin Environment of Quantum Dots Invited Speaker: Electrons in semiconductor quantum dots typically interact with a large ensemble of surrounding nuclear spins via hyperfine coupling. When uncontrolled, this coupling can produce rapid dephasing of electron spin degrees of freedom. These effects of nuclear spin environment were recently observed in several experiments. We describe several approaches to control the interaction between electronic and nuclear degrees of freedom, which allow one to eliminate the dephasing associated with nuclei and to use the localized ensembles of nuclear spins as a useful resource. These approaches make use of the long-lived memory associated with nuclear spins. In particular, we will describe a technique for storing electronic spin qubits in collective states of nuclear ensembles. This can be achieved by controlling hyperfine interaction with external effective magnetic fields, and can result in a robust quantum memory for mesoscopic quantum bits with potential coherence times approaching seconds. Potential applications of this technique for long-distance quantum communication and scalable quantum computation will be discussed. [Preview Abstract] |
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